public BackupViewModel(Backup backup, RepositoryManager repositoryManager, IDialogService dialogService)
        {
            this.backup = backup;
            this.repositoryManager = repositoryManager;
            this.dialogService = dialogService;

            BackupCommand = new RelayCommand(CreateBackup);
            RestoreCommand = new RelayCommand(RestoreBackup);
        }
        public BackupViewModel(RepositoryManager repositoryManager,
            IBackupService backupService,
            IDialogService dialogService)
        {
            this.repositoryManager = repositoryManager;
            this.dialogService = dialogService;

            BackupService = backupService;
        }